1. Field of the Invention
The present invention relates to a process for manufacturing a hollow turbomachine blade, particularly a large-chord fan rotor blade, and to a progressive hot twisting apparatus for use in the process.
The advantages of using large-chord blades in turbomachines are particularly evident in the case of the fan rotor blades in bypass turbojet engines. These blades must, however, withstand severe conditions of use and, in particular, must possess satisfactory mechanical characteristics associated with antivibratory properties and resistance to impact by foreign bodies. The need for sufficiently high velocities at the tips of the blades has also led to research into reducing the mass of the blades, and this has been achieved, in particular, by the use of hollow blades.
2. Discussion of the Background
EP-A-0700738 describes a process for manufacturing a hollow turbomachine blade, especially a large-chord fan rotor blade. In this known process a first step (a) is to use a computer-aided design and manufacture (CAD/CAM) system to create, starting from the geometric definition of the blade to be obtained, a digital simulation of the primary parts of the blade in flat form and including a computation, for each part, of the lengths of the fibers on each side of the central fiber as a function of their position with respect to the axis of the part. Also carried out at this stage is a digital simulation of an operation to shape the parts by twisting, for comparison with the final result. After this first step EP-A-0700738 teaches a general operating procedure involving the following steps:
(b) die-forging the primary parts of the blade using a press; PA1 (c) machining the primary parts; PA1 (d) depositing diffusion barriers on at least one of the parts according to a predefined pattern; PA1 (e) assembling the primary parts and diffusion welding them together under isostatic pressure; PA1 (f) pressurized gas inflation and superplastic shaping of the welded assembly; and, PA1 (g) final machining of the assembly. PA1 a metallic support structure; PA1 a cylindrical electric furnace fixed vertically on said support structure, said furnace having a wall including a plurality of horizontal slots; PA1 a circular frame surrounding said furnace; PA1 a plurality of rings which are free to rotate about said frame; PA1 bars disposed on said rings and projecting inwards through said slots in said furnace wall so as to act on the collars attached to the element which is to be twisted when said element is placed in said furnace; and PA1 jaws for gripping opposite ends of said element to hold said element in position in said furnace and enabling a tensile force to be applied to said element along the axis thereof during twisting of said element.
One of the aims of the invention is to make it possible to carry out, during the above sequence of operations, an additional shaping of the parts by twisting, without the risk of causing buckling-type undulations along the central fiber. These undulations are generated by compressive stresses induced during elongation of the lateral fibers as a result of the differences in length between the initial flat part and the twisted part which is obtained.